Background
[0001] This invention relates generally to a method for purification of triglycerides used
as raw materials for biodiesel fuel production.
[0002] High fuel prices and environmental concerns are driving development of alternative
fuels, especially those derived from renewable resources. One such fuel, commonly
known as "biodiesel" fuel, commonly contains methyl esters of fatty acids, and is
burned in diesel engines. One source of biodiesel fuel is transesterification of triglycerides,
such as vegetable oils with alcohols, typically with methanol. As the cost of raw
materials keeps rising for the biodiesel industry, it is becoming more important to
use a variety of crude, recycled, and non-edible triglyceride starting materials.
These materials can be, for example, crude palm oil, yellow grease (waste restaurant
grease), waste animal fat, algae oil, Jatropha oil etc. However, these materials contain
many, and varied impurities which are unsuitable for the biodiesel process and undesirable
in the fuel. Prior art methods exist for purification of oils, e.g.,
U.S. Pat. No. 6,960,673. However, the resultant oil from these methods may still contain high levels of impurities,
namely, proteins, dissolved ions, residual phospholipids, vitamins, sterol glucosides,
etc.
[0003] The problem addressed by this invention is to find an alternative method for purification
of triglycerides used as raw materials for production of biodiesel fuels.
Statement of Invention
[0004] The present invention is directed to a method for purification of crude triglycerides
to be used as a raw material for production of biodiesel fuel. The method comprises
steps of contacting a crude triglyceride stream with the following materials: (a)
at least one adsorbent; (b) at least one phenolic resin, metal-containing resin or
hydrous metal oxide; and (c) at least one cation exchange resin.
Detailed Description
[0005] All percentages are weight percentages ("wt %"), and all temperatures are in °C,
unless otherwise indicated. Weight percentages related to ion exchange resins or other
resins are based on dry resin. As used herein the term "(meth)acrylic" refers to acrylic
or methacrylic. The term "vinyl monomer" refers to a monomer suitable for addition
polymerization and containing a single polymerizable carbon-carbon double bond. The
term "styrene polymer" or "styrenic polymer" indicates a copolymer polymerized from
a vinyl monomer or mixture of vinyl monomers containing at least one styrene monomer
(styrene or substituted styrene) and/or at least one crosslinker, wherein the combined
weight of styrene monomers and crosslinkers is at least 50 wt % of the total monomer
weight, alternatively at least 75 wt %, alternatively at least 90 wt %. Styrene monomers
include, e.g., styrene, α-methylstyrene, and ethylstyrene. A crosslinker is a monomer
containing at least two polymerizable carbon-carbon double bonds, including, e.g.,
divinylaromatic compounds, di- and tri-(meth)acrylate compounds and divinyl ether
compounds. Preferably, the crosslinker(s) is a divinylaromatic crosslinker, e.g.,
divinylbenzene. In one embodiment, a styrene polymer is made from a mixture of monomers
that is at least 75% styrene and divinylaromatic crosslinkers, more preferably at
least 90% styrene and divinylaromatic crosslinkers, and most preferably from a mixture
of monomers that consists essentially of styrene and at least one divinylaromatic
crosslinker. In another embodiment, a styrene polymer is made from a monomer mixture
consisting essentially of at least one divinylaromatic crosslinker. The term "acrylic
polymer" indicates a copolymer formed from a mixture of vinyl monomers containing
at least one (meth)acrylic acid or ester, along with at least one crosslinker, wherein
the combined weight of the (meth)acrylic acid(s) or ester(s) and the crosslinker(s)
is at least 50 weight percent of the total monomer weight; preferably at least 75%,
more preferably at least 90%, and most preferably from a mixture of monomers that
consists essentially of at least one (meth)acrylic acid or ester and at least one
crosslinker. The term "phenolic resin" indicates a crosslinked copolymer formed from
an aliphatic aldehyde or ketone (e.g., formaldehyde) and phenol or a substituted phenol,
or other aromatic compound, wherein the weight of phenol or substituted phenol monomer
is at least 20% of the total monomer weight, alternatively at least 50%, alternatively
at least 70%.
[0006] The term "gel" resin applies to a resin which was synthesized from a very low porosity
(0 to 0.1 cm
3/g), small average pore size (0 to 17 Å) and low B.E.T. surface area (0 to 10 m
2/g) copolymer. The term "macroreticular" (or MR) resin is applied to a resin which
is synthesized from a high mesoporous copolymer with higher surface area than the
gel resins. The total porosity of the MR resins is between 0.1 and 0.7 cm
3/g, average pore size between 17 and 500 Å and B.E.T. surface area between 10 and
200 m
2/g. The term adsorbent resin is applied to a resin which can be functionalized or
not, and which has very high surface area and porosity. These adsorbents have surface
area between 200 and 1900 m
2/g, average pore size between 17 and 1000 Å and total porosity between 0.7 and 200
cm
3/g. The term "cation exchange resin" indicates a resin which is capable of exchanging
positively charged species with the environment. They comprise negatively charged
species which are linked to metal cations. The most common negatively charged species
are carboxylic, sulfonic and phosphonic acid groups. The term "anion exchange resin"
indicates a resin which is capable of exchanging negatively charged species with the
environment. The term "strong base anion exchange resin" refers to an anion exchange
resin that comprises positively charged species which are linked to anions. The most
common positively charged species are quaternary amines and protonated secondary amines.
Preferably, resins are in the form of commercially available resin beads having a
harmonic mean size from 50 microns to 1500 microns, alternatively from 150 to 900
microns, alternatively from 300 to 600 microns. In some embodiments of the invention,
resins are commercially available uniform particle size resin beads. The term "crude
triglyceride stream" applies to the stream comprising triglyceride material flowing
through the various purification media described herein. The crude triglyceride stream
may, after treatment with several media, be substantially more pure than the starting
crude triglyceride, but the same term is used to designate the stream throughout the
process.
[0007] Adsorbents useful in this invention are resins having surface area between 200 and
1900 m
2/g, average pore size between 17 and 1000 Å and total porosity between 0.7 and 200
cm
3/g. Adsorbent resins include, e.g., phenolic, styrenic and acrylic resins. In some
embodiments of the invention, the crude triglyceride stream is contacted with a styrenic
adsorbent resin to remove proteins and a phenolic adsorbent resin to remove sterol
glucosides. In a preferred embodiment of the invention, the styrenic adsorbent resin
is a macroreticular resin, and the phenolic adsorbent resin has weakly basic anion
exchange functionality. An example of a styrenic adsorbent resin is AMBERLITE™ XAD-16
(available from Rohm and Haas Co.). An example of a phenolic adsorbent resin is AMBERLITE™
XAD-761 (available from Rohm and Haas Co.).
[0008] In some embodiments of the invention, the cation exchange resin has carboxylic acid
functionality ("weak acid" resin); in some embodiments it is a macroporous resin.
In some embodiments of the invention, the resin is a cross-linked acrylic resin, preferably
one cross-linked with divinylbenzene, e.g., a resin made from methacrylic acid and
divinylbenzene. Examples of such resins are AMBERLITE™ IRC-50 and IR-120H (available
from Rohm and Haas Co.).
[0009] In some embodiments of the invention, the cation exchange resin has sulfonic acid
functionality ("strong acid" resin); in some embodiments it is a macroporous resin.
In some embodiments, the resin is a crosslinked styrenic gel resin, e.g., a resin
made from styrene and divinylbenzene, and functionalized by sulfonation.
[0010] A "metal-containing resin" is a resin containing at least one metal compound. Preferred
metals include iron, aluminum, manganese, zirconium and titanium. In some embodiments
of the invention, the metal-containing resin has from 2% to 35% metal, on a dry resin
basis. In some embodiments, the metal content of the resin is at least 5%, alternatively
at least 8%, alternatively at least 10%, alternatively at least 12%, alternatively
at least 15%, alternatively at least 20%; the metal content is no greater than 30%,
alternatively no greater than 28%, alternatively no greater than 25%. A preferred
form for the metal is the hydrous oxide form, i.e., very insoluble compounds in water
which are formed from the precipitation of a metal cation with a pH increase in the
original solution. The hydrous oxide may be essentially oxides or hydroxides of a
single metal or of a mixture of two or more metals. The charge on a hydrous oxide
species depends largely upon the degree of acidity of the oxide and the media. They
can exist as negatively, neutral or positively charged species. Variations in precipitation
conditions for metal ions can result in different structures that can be relatively
more or less reactive. The structure of the metallic hydrous oxides can be amorphous
or crystalline.
[0011] In some embodiments of the invention, the resin used to support the metal is an acrylic
resin functionalized with the functional group shown below:
RR
1N{(CH
2)
xN(R
2)}
z(CH
2)
yNR
3R
4
where R denotes the resin, to which the amine nitrogen on the far left is attached
via an amide bond with an acrylic carbonyl group or via a C-N bond to a CH
2 group on the acrylic resin; R
1 and R
2=H, Me or Et; x and y =1-4, z = 0-2 and R
3 and R
4 = Me, Et, Pr or Bu. A more preferred functionalization would have R attached via
an amide bond; R
1=H or Me; z = 0 ; y = 1-4 and R
3 and R
4 = Me or Et. The most preferred embodiment would have R
1=H; y = 3 and R
3 and R
4 = Me. The amine functional group can be introduced by reacting a diamine which is
alkylated on one end, e.g., 3-dimethylaminopropylamine (DMAPA) with the acrylic resin
at high temperature (e.g., 170-189°C), under nitrogen pressure (e.g., between 35-60
psig (241-413 kPa)) for 8-24 hours.
[0012] In some embodiments of the invention, the phenolic resin, metal-containing resin
or hydrous metal oxide is a hydrous metal oxide, e.g., ferric hydrous oxide or titanium
hydrous oxide, either amorphous or crystalline. Preferably, hydrous metal oxide adsorbents
have average particle sizes from 50 microns to 4 mm, alternatively from 150 microns
to 1 mm. Preferably, the porosity is from 15 m
2/g to 700 m
2/g, alternatively from 100 m
2/g to 350 m
2/g.
[0013] In some embodiments of the invention, the crude triglyceride stream which has passed
through: (a) at least one adsorbent; (b) at least one phenolic resin, metal-containing
resin or hydrous metal oxide; and (c) at least one cation exchange resin is carried
on to a transesterification process without further purification. In some embodiments
of the invention, further purification steps are performed prior to transesterification.
[0014] In some embodiments of the invention, the crude triglyceride stream is further contacted
with an anion exchange resin. The resin may be a weak base or strong base anion exchange
resin. In some embodiments, the resin is either an acrylic resin or a styrenic resin.
[0015] In some embodiments of the invention, the crude triglyceride stream is further contacted
with alumino-silicate adsorbents containing alumina, silica or a combination thereof,
including, e.g., alumina, silica, quartz, feldspar, Celite, diatomaceous earth, rice
husk ash, zeolite and andalusite. Preferably, the alumino-silicate adsorbents have
average particle sizes from 100 microns to 2 mm, more preferably from 250 microns
to 1 mm. Preferably, the porosity of the alumino-silicate adsorbents is from 45 m
2/g to 1800 m
2/g, more preferably from 150 m
2/g to 1500 m
2/g.
[0016] "Triglycerides" used in this invention are fats or oils comprising glycerine triesters
of fatty acids. Fatty acids are acyclic aliphatic carboxylic acids containing from
8 to 22 carbon atoms; typically, they contain from 12 to 22 carbon atoms. With respect
to carbon-carbon bonds, the fatty acid chains may be saturated, monounsaturated or
polyunsaturated (typically 2 or 3 carbon-carbon double bonds). Natural fats may also
contain small amounts of other esterified, or free fatty acids, as well as small amounts
(1-4%) of phospholipids, e.g., lecithin, and very small amounts (<1%) of other compounds,
e.g., tocopherols. Crude triglycerides also may contain a variety of other impurities,
e.g., carotenes, sterols, phospholipids, salts, sterol glucosides, proteins, amino
acids and vitamins. In some embodiments of the invention, crude triglycerides are
animal fats.
[0017] In some embodiments of the invention, the purification of crude triglycerides is
performed in a temperature range from about 20°C to 150°C. In some embodiments of
the invention, the temperature is no greater than 130°C, alternatively no greater
than 110°C, alternatively no greater than 100°C, alternatively no greater than 90°C,
alternatively no greater than 80°C. In some embodiments of the invention, the temperature
is at least 30°C, alternatively at least 40°C, alternatively at least 50°C, alternatively
at least 55°C, alternatively at least 60°C. The higher temperatures listed above generally
are required for higher molecular weight triglycerides or other triglycerides with
high melting points.
[0018] Typical flow rates for treatment of crude triglycerides according to this invention
are from 0.05 to 50 bed volumes ("BV")/hour. In some embodiments of the invention,
the flow rate is at least 0.2 BV/hour, alternatively at least 2 BV/hour. In some embodiments
of the invention, the flow rate is no more than 30 BV/hour, alternatively no more
than 10 BV/hour. Flow rates through the various materials would be similar, but not
necessarily the same.
[0019] The uniformity coefficient of an ion exchange resin bead particle size distribution
is a measure of the width of the size distribution curve. The uniformity coefficient
is defined as d60/d10 where d60 is the size of the opening through which exactly 60
volume % of the distribution passes, and d10 is the size of the opening through which
exactly 10 volume % of the distribution passes. In some embodiments of the invention,
the uniformity coefficient of the resin beads is no greater than 1.15, alternatively
no greater than 1.10.
[0020] In some embodiments of the invention, the crude triglycerides contact an adsorbent
resin before any other resin or hydrous metal oxide. In some embodiments of the invention,
the crude triglycerides contact a phenolic resin, metal-containing resin or hydrous
metal oxide after the adsorbent resin and before any other resin.
[0021] In some embodiments of the invention, a C
1-C
4 aliphatic alcohol is added to the crude triglyceride stream during the process. This
facilitates direct transfer of the crude triglyceride stream to a reactor for transesterification.
Suitable alcohols include, e.g., methanol, ethanol, propanol, isopropanol, butanol
and isobutanol. Methanol is especially preferred.
1. A method for purification of crude triglycerides to be used as a raw material for
production of biodiesel fuel; said method comprising contacting a crude triglyceride
stream with:
(a) at least one adsorbent; (b) at least one phenolic resin, metal-containing resin
or hydrous metal oxide; and (c) at least one cation exchange resin.
2. The method of claim 1 in which an adsorbent is a resin having a surface area between
200 and 1900 m2/g, average pore size between 17 and 1000 Å and total porosity between 0.7 and 200
cm3/g.
3. The method of claim 2 in which the crude triglyceride stream contacts an adsorbent
resin before any other resin or hydrous metal oxide.
4. The method of claim 3 in which the crude triglyceride stream contacts a phenolic resin,
metal-containing resin or hydrous metal oxide after the adsorbent resin and before
any other resin.
5. The method of claim 4 in which the crude triglycerides are animal fats.
6. The method of claim 5 in which said at least one phenolic resin, metal-containing
resin or hydrous metal oxide is a metal-containing resin.
7. The method of claim 6 in which the metal comprises iron.
8. The method of claim 7 further comprising contacting the crude triglyceride stream
with at least one alumino-silicate adsorbent.
9. The method of claim 7 further comprising contacting the crude triglyceride stream
with at least one anion exchange resin.